COMPARISON OF CURRENT WAVE-FORMS FOR THE ELECTRICAL-STIMULATION OF RESIDUAL LOW-FREQUENCY HEARING

Many cochlear prostheses employ charge-balanced biphasic current pulse s. These pulses have little energy at low frequencies resulting in lim ited stimulation of low frequency hearing by mechanical responses to t he electrical stimulus. However, if electro-mechanical transduction wi thin the cochlea is nonlinear, electrical stimulation with asymmetric, charge-balanced current pulses may result in a mechanical response wi th significantly more low frequency energy. We estimated the mechanica l response at low frequencies to pulsatile electrical stimulation of t he cochlea. The auditory nerve compound action potential evoked by low frequency tones was forward-masked by a train of symmetric or asymmet ric current pulses. Masking by asymmetric current pulses was not signi ficantly different from masking by symmetric pulses matched for pulse duration and charge. In conclusion, there appears to be no advantage t o using asymmetric current pulses for the mechanical stimulation of re sidual low frequency hearing by electrical stimulation of the cochlea.